1969 T-bird pressure build in the radiator

Need help to resolve my issue. 429 CID - as soon as I start the car there is immediate pressure build in the radiator. Running engine for 10 seconds creates pressure and some heat. The car has set since 1982. Is it possible the water pump is ceased or head gasket blown. Seems no milky oil issue. Ran hose water through top hose and water does circulate. What is possible issue. Engine has 120,000 miles.